There is also the possibility of using multiple first person points of view
I've read two novels where there were 2 first-person points of view used. The first was Mothernight, by Sarah Stovell (who used to be on here - is she still?). The other was Allegiant, which is the third of the Divergent trilogy. In Mothernight, it worked really well, as the two voices were divided up neatly so that you could see who was saying what. In Allegiant, it jarred a little, possibly because the first two books in the trilogy stick strictly to a single POV. So I think it can be done, if handled well, but it requires careful handling, and possibly even more careful planning to work out whether it's right for the story.